JP2016537681A - Illumination system for EUV projection lithography - Google Patents

Abstract

The illumination system for EUV projection lithography has a beam shaping optical unit (6) for generating an EUV collective output beam (7) from an EUV raw beam (4) of a synchrotron radiation-based light source (2). The output coupling optical unit (8) functions to generate a plurality of EUV individual output beams (9i) from the EUV collective output beam (7). In each case, the beam guiding optical unit (10) functions to guide the respective EUV individual output beam (9i) towards the object field (11) where a lithographic mask (12) can be placed. The result is an illumination system used to flexibly guide the EUV light of a synchrotron radiation-based light source to the maximum possible without loss and at the same time. [Selection] Figure 1

Description

  The content of German Patent Application No. 10 2013 223 935.1 is hereby incorporated by reference.

  The present invention relates to a deflection optical unit for an illumination system for EUV projection lithography. The present invention relates to a beam shaping optical unit and a beam guiding optical unit for an illumination system for EUV projection lithography. In addition, the present invention relates to an illumination system for EUV projection lithography and a projection exposure apparatus for EUV lithography. Finally, the present invention relates to a method for generating a structured component and a structured component generated according to the method.

  Projection exposure apparatus including illumination systems are known from US 2011/0 014 799 A1, WO 2009/121 438 A1, US 2009/0 174 876 A1, US 6,438,199 B1, and US 6,658,084 B2. It is. EUV light sources are known from DE 103 58 225 B3 and US 6,859,515 B. Further components for EUV projection lithography are known from US 2003/0002022 A1, DE 10 2009 025 655 A1, US 6,700,952 and US 2004/0140440 A. Yet another reference in which EUV light sources are known is found in WO 2009/121 438 A1. EUV illumination optical units are known from US 2003/0043359 A1 and US 5,896,438.

German Patent Application No. 10 2013 223 935.1 US 2011/0 014 799 A1 WO 2009/121 438 A1 US 2009/0 174 876 A1 US 6,438,199 B1 US 6,658,084 B2 DE 103 58 225 B3 US 6,859,515 B US 2003/0002022 A1 DE 10 2009 025 655 A1 US 6,700,952 US 2004/0140440 A US 2003/0043359 A1 US 5,896,438 US 2007/0152171 A1 EP 1 072 957 A2 US 6 198 793 B1

Uwe Schindler, “Electric supersonic undulator with electronically switchable helicity” (Heldholtz Institute Karlsruhe Research Center, Science Report FZKA69, April 1997) H. Wolter, "Spigelsysteme Eifnsalls abblende Optiken fur Rongenstrahlen", p. 94, p. 94, p. 49, p.

  It is an object of the present invention to provide a deflecting optical unit for an illumination system for EUV projection lithography such that it provides a lossless and flexible guidance of the EUV light of a synchrotron radiation-based light source to the maximum possible extent. To develop a beam shaping optics unit, a beam guidance optics unit, and an illumination system for EUV projection lithography.

  According to the invention, these objects are achieved by a deflection optical unit having the features of claim 1, a beam guiding optical unit having the features of claim 3, a beam shaping optical unit having the features of claim 5, And an illumination system having the features of claim 10.

  The beam guidance of EUV light or EUV radiation supplied by a synchrotron radiation-based light source requires specific adjustments due to the properties of the EUV raw beam emitted by such a light source. This adjustment is ensured by the beam shaping optical unit according to the invention, the output coupling optical unit and the beam guiding optical unit, and also by the individual beam guiding components, ie the deflection optical unit and the focus assembly.

The synchrotron radiation-based light source can be a free electron laser (FEL), undulator, wiggler, or x-ray laser. A synchrotron radiation-based light source can have an etendue smaller than 0.1 mm ² or even smaller. The optical unit according to the invention can generally be operated with the emitted light of a light source having such a small etendue, whether or not a synchrotron radiation-based light source is included.

  The beam shaping optical unit allows pre-shaping of the collective output beam from the raw beam to prepare for subsequent output combination in the individual output beams by the output combining optical unit. Individual output beams are guided to their respective object fields by a beam guiding optical unit. This offers the possibility of illuminating multiple object fields with one and the same synchrotron radiation-based light source, thereby generating fine or nanostructured components, for example semiconductor chips, in particular memory chips The possibility of supplying a plurality of projection exposure apparatuses that can be used with one same synchrotron radiation-based light source is provided.

  By using an output coupling optical unit and a downstream beam guiding optical unit, a variable intensity distribution can be ensured for the amount of radiation power in the various EUV individual output beams. Accordingly, adaptation to the number of projection exposure apparatuses supplied with light and adaptation to the refractive power required by each projection exposure apparatus can be performed. Thus, in this case, the various requirements of the refractive power each required for creating a particular structure can be met by the corresponding adaptation of the illumination system.

  The deflection optical unit according to claim 1 results in a low loss of EUV radiation deflected thereby.

  The grazing incidence mirror is designed for an angle of incidence greater than 60 °. This incident angle can be even greater.

  At least one of the grazing incidence deflection mirrors can be embodied as a convex cylindrical mirror. At least one of the grazing incidence deflection mirrors can be embodied as a concave cylindrical mirror. Embodiments of the deflecting optical unit can include a greater number of concave cylindrical mirrors than convex cylindrical mirrors.

  An EUV beam incident in parallel to the deflection optical unit, in particular an EUV individual output beam, can have a divergence of less than 1 mrad after exiting the deflection optical unit. Such a design of the deflection optical unit makes it possible to guide the EUV beam over a large distance.

  In the case of the deflecting optical unit according to claim 2, the aspect ratio contribution of the beam guiding optical unit generated thereby can be adapted to a predetermined value. As an example, the magnification ratio for the aspect ratio can be changed between a value 4 and a value 5 or between a value 1.5 and a value 2 in a particularly continuously variable manner. At least one of the grazing incidence deflection mirrors of the deflection optical unit can be embodied to have a radius of curvature that is variable in a driven manner. As a result, a further adaptation of the optical effect of the deflection optical unit to a predetermined value can be achieved.

  In the case of the beam shaping optical unit according to claim 4, the group incidence planes can be perpendicular to each other. The mirror group of the beam shaping optical unit can include two mirrors, three mirrors, or more mirrors. The use of more mirror groups with different group incidence planes allows to influence EUV radiation independently in two lateral dimensions to produce the desired aspect ratio.

  The mirror group can be designed by the Galileo telescope method.

  The mirror of the beam shaping optical unit can be embodied as a convex or concave cylindrical mirror, for example.

  The grazing incidence mirror is designed for an angle of incidence greater than 60 °. The incident angle can be even greater.

  The arrangement according to claim 5 offers the possibility, for example, of providing a large distance between the mirrors of one and the same group of mirrors which have to be given a large magnification in order to produce the desired aspect ratio.

  The incident angle of EUV radiation according to claim 6 enables optimization of the transmission rate for EUV radiation as it passes through the beam shaping optical unit.

  The incident angle according to claim 7 increases flexibility in the design of the beam shaping optical unit, for example, adapting the grazing incidence to a predetermined beam diameter of the incident EUV beam so that the mirror size remains in a predetermined dimension range. Enable.

  The design of the beam shaping optical unit according to claim 8 makes it possible, for example, to horizontally guide both the beam incident in the beam shaping optical unit and the beam emerging from the beam shaping optical unit.

  The divergence of the EUV collective output beam can be less than half of the divergence of the EUV raw beam. The corresponding design of the beam shaping optical unit makes it possible to guide the EUV collective output beam over a large distance.

  The at least one mirror of the beam shaping optical unit can have a deviation of at least 5 μm from the optimal fitting cone. At least one mirror of the beam shaping optical unit can be embodied as a free-form surface. The corresponding mirror design of the beam shaping optical unit increases the degree of freedom in adapting the optical effect of the beam shaping optical unit to a predetermined value.

  The beam guiding optical unit according to claim 9 makes it possible to guide the EUV radiation through a relatively small passage opening through the diaphragm or wall. This allows the desired separation between the various chambers in which EUV radiation is guided. In addition to this, it is possible to use an assembly of a projection exposure apparatus aligned with the intermediate focus of EUV illumination light having a predetermined numerical aperture downstream of the intermediate focus.

  The focus assembly according to claim 10 can be embodied in the form of a type I, type II, or type III Walter mirror group. At least two mirrors of the focus assembly can be sequentially placed in the beam path of the EUV individual output beam.

  The focus assembly can be implemented such that the structural space of the focus assembly along the beam path of the EUV individual output beam is approximately twice the size of the major half axis of the ellipsoidal mirror of the focus assembly. The focus assembly can be implemented such that the structural space of the focus assembly along the beam path of the EUV individual output beam is about 50 times the size of the diameter of the EUV individual output beam as it enters the focus assembly. . When NA represents the numerical aperture at the intermediate focus of the focus assembly, the focus assembly is 0.7 NA <b / a with respect to the ratio b / a of the minor semi-axis b of the ellipsoidal mirror to the major semi-axis a of the ellipsoidal mirror. <0.9NA can be realized.

  The focus assembly includes at least one paraboloidal mirror and is embodied such that a / f> 50 with respect to the ratio a / f between the major axis a of the ellipsoidal mirror and the focal length f of the parabolic mirror. be able to.

  The focus assembly can be implemented such that the minimum deflection angle experienced by the peripheral rays of the EUV individual output beam passing through it is not greater than 5 °.

  The above objective is accomplished with an illumination system comprising a beam shaping optical unit, an output coupling optical unit, and in each case a beam guiding optical unit. The beam shaping optical unit, the output coupling optical unit, and / or the beam guiding optical unit can be implemented in particular according to the above description. These advantages are apparent from the description of each component.

  An illumination system comprising a beam shaping optical unit and an output coupling optical unit according to claim 11 makes it possible to provide a plurality of EUV individual output beams having a predetermined aspect ratio of the EUV beam diameter. The aspect ratio contribution provided on the one hand by the beam shaping optics unit and on the other hand by the output coupling optics unit and its downstream beam guiding optics unit is a desired set aspect ratio, e.g. the aspect ratio of the illuminated object field. You can multiply. The generation of 1: 1 desired aspect ratio contributions for multiple individual output beams starting from the raw beam is initially allocated to the generation of aspect ratio contributions not equal to 1 by the beam shaping optics unit, to multiple individual output beams. This is due to the generation of the corresponding aspect ratio contribution by the output coupling optical unit and the beam guiding optical unit after splitting the collective output beam. This allows the aspect ratio change that is forced by the various optical assemblies through which the EUV beam passes on the path of the EUV illumination light from the light source to the object field to be a gentle change. Alternatively, the beam shaping optics unit can be used first to produce different aspect ratio contributions, eg, 1: N aspect ratio contributions for N EUV individual output beams. . In this case, the downstream output coupling optics unit must nevertheless split the EUV collective output beam thus generated, but in each case an EUV individual output with a 1: 1 aspect ratio contribution. The unit's unique aspect ratio effect is not required to predetermine the beam. To generate N number of EUV individual output beams with 1: 1 aspect ratio contribution in each case, on the one hand the aspect ratio contribution generated by the beam shaping optical unit and on the other hand the output coupling optical unit and the beam guiding optics. Different distributions of the aspect ratio contribution produced by the unit are possible.

  Advantages of the projection exposure apparatus according to claim 14, the generation method according to claim 15 and the structured component according to claim 16 correspond to those described above with reference to the preceding claims.

  The light source of the illumination system can be a free electron laser (FEL), undulator, wiggler, or X-ray laser.

  The EUV collective output beam can have an intensity distribution that deviates by less than 10% from uniform intensity at all points in the range of the working cross section. Each EUV individual output beam can have a corresponding uniformity downstream of the deflection optics unit.

  All mirrors of the illumination system can carry a highly reflective coating.

  The beam shaping optical unit, the deflection optical unit, and the focus assembly are essential assemblies for the present invention, both autonomously, i.e. without further assembly of the illumination system.

  All the features of the claims can be combined with each other in different combinations.

  Exemplary embodiments of the invention are described in more detail below with reference to the drawings.

1 is a schematic view of a projection exposure apparatus for EUV projection lithography. For the system of the projection exposure apparatus of FIG. 1 proceeding downstream of an output combining optical unit for generating a plurality of individual output beams from an EUV collective output beam from an EUV light source for generating an EUV raw beam FIG. 6 is a similar schematic diagram showing the guidance section of the EUV beam path. It is a figure which shows the cross-sectional ratio of the EUV radiation in the middle of the EUV beam path | route between the light guide and the beam guide in the illumination optical unit arrange | positioned upstream of the object visual field of a projection exposure apparatus. It is a side view of a beam shaping optical unit for generating an EUV collective output beam from an EUV raw beam. FIG. 5 is still another side view from the direction V in FIG. 4. FIG. 5 is a very schematic diagram showing the beam shaping optical unit of FIG. 4 for revealing the deflection angle caused by the mirror of the beam shaping optical unit. FIG. 6 is a very schematic diagram showing the beam shaping optical unit of FIG. 5 for revealing the deflection angle caused by the mirror of the beam shaping optical unit. FIG. 8 is a view similar to FIGS. 6 and 7 showing yet another embodiment of the beam shaping optical unit. FIG. 8 is a view similar to FIGS. 6 and 7 showing yet another embodiment of the beam shaping optical unit. FIG. 8 is a view similar to FIGS. 6 and 7 showing yet another embodiment of the beam shaping optical unit. FIG. 8 is a view similar to FIGS. 6 and 7 showing yet another embodiment of the beam shaping optical unit. A beam shaping optical unit and a deflection arranged downstream of the output coupling optical unit in the beam path of the EUV individual output beam as part of the beam guiding optical unit for guiding the respective EUV individual output beam towards the object field FIG. 3 is a slightly more detailed view showing the EUV beam path to and from the optical unit than in the case of FIGS. 1 and 2. Parallel to the incident plane on the deflection mirror showing an embodiment of the deflection optical unit comprising the first two convex cylindrical mirrors, one downstream plane mirror, and three downstream concave cylinder mirrors in the beam path of the EUV individual output beam It is a very schematic cross-sectional view. FIG. 14 is a view similar to FIG. 13 illustrating yet another embodiment of a deflection optical unit including one convex cylindrical mirror and three concave cylindrical mirrors that follow in sequence in the EUV beam path. FIG. 14 is a view similar to FIG. 13 showing yet another embodiment of a deflection optical unit including one convex cylinder mirror, one plane mirror, and two concave cylinder mirrors arranged in series in the EUV beam path. . FIG. 14 is a view similar to FIG. 13 showing yet another embodiment of a deflection optical unit including one convex cylinder mirror, one plane mirror, and three concave cylinder mirrors arranged in series in the EUV beam path. . Yet another embodiment of a deflecting optical unit comprising one convex cylindrical mirror, two downstream concave cylindrical mirrors, one downstream planar mirror, and two downstream concave cylindrical mirrors arranged in series in the EUV beam path. It is a figure similar to FIG. FIG. 13 shows yet another embodiment of the deflecting optical unit comprising one convex cylindrical mirror, one downstream plane mirror, and four concave cylindrical mirrors successively following downstream arranged in series in the EUV beam path. It is a similar figure. Fig. 6 shows yet another embodiment of a deflection optical unit comprising one convex cylindrical mirror arranged in tandem in the EUV beam path, two planar mirrors sequentially downstream, and three concave cylindrical mirrors sequentially downstream. It is a figure similar to FIG. Among the EUV individual output beams between the deflection optical unit and the intermediate focal plane for clarifying the function of the focus assembly of the beam guiding optical unit or the input coupling optical unit for guiding each EUV individual output beam to the object field FIG. 3 is an excerpt from the beam path of one of It is a figure similar to FIG. 20 which shows another embodiment of an input coupling optical unit. FIG. 2 shows an embodiment of a Walter I type input coupling optical unit. FIG. 2 shows an embodiment of a Walter type II input coupling optical unit. FIG. 3 shows an embodiment of a Walter III type input coupling optical unit. FIG. 6 shows yet another embodiment of a Walter type III input coupling optical unit. FIG. 6 shows one of various modifications of the beam shaping optical unit. FIG. 6 shows one of various modifications of the beam shaping optical unit. FIG. 6 shows one of various modifications of the beam shaping optical unit. It is the schematic of a beam expansion component.

  A projection exposure apparatus 1 for microlithography is a part of a system including a plurality of projection exposure apparatuses, and FIG. 1 shows one of the projection exposure apparatuses. The projection exposure apparatus 1 functions to generate fine or nanostructured electronic semiconductor components. A common light source or radiation source 2 for all projection exposure apparatuses of the system emits EUV radiation with a wavelength in the range, for example, between 2 nm and 30 nm, in particular between 2 nm and 15 nm. The light source 2 is embodied as a free electron laser (FEL). The light source 2 includes a synchrotron radiation source or a synchrotron radiation-based light source that generates coherent radiation with very high brightness. A publication describing such FELs is given in WO 2009/121 438 A1. The light source 2 that can be used is “Superconductive undulator with electrically switchable helicity” by Uwe Schindler, “Helmholtz Institute Karlsruhe F, Research Center A, Karlsruhe Research Center A,” August 2007, US 2007/0152171 A1, and DE 103 58 225 B3.

The light source 2 has an original etendue smaller than 0.1 mm ² in the raw beam. Etendue is the minimum phase space volume that contains 90% of the emitted light energy of the light source. The definition of etendue corresponding to this etendue is found in EP 1 072 957 A2 and US 6 198 793 B1, where these x and y are the field dimensions that span the illuminated illumination field and NA is When the numerical aperture of the field illumination is obtained, it is obtained by multiplying the illumination data x, y and NA ² . Etendues smaller than 0.1 mm ^{2 of the} light source are possible, for example etendues smaller than 0.01 mm ² .

  The EUV light source 2 includes an electron beam supply device for generating an electron beam and an EUV generation device. The EUV generation device is supplied with an electron beam by an electron beam supply device. The electron beam delivery device is embodied as an undulator. Optionally, the undulator can include an undulator magnet that is adjustable by displacement. The undulator can include an electromagnet. In the case of the light source 2, a wiggler can be provided.

  The light source 2 has an average power of 2.5 kW. The pulse frequency of the light source 2 is 30 MHz. Each individual radiation pulse delivers 83 μJ of energy. For a radiation pulse length of 100 fs, this corresponds to a radiation pulse power of 833 MW.

  The number of repetitions of the light source 2 is, for example, 100 kHz in the kilohertz range, for example, 3 MHz in the relatively low megahertz range, for example, 30 MHz in the moderate megahertz range, for example, 300 MHz in the upper megahertz range, or other gigahertz For example, the range may be 1.3 GHz.

  In the following, an orthogonal xyz coordinate system is used to facilitate the illustration of the positional relationship. Usually, in these examples, the x coordinate stretches the beam cross section of the EUV illumination imaging light 3 together with the y coordinate. Accordingly, the z direction normally extends in the beam direction of the illumination imaging light 3. For example, in FIG. 2 and FIG. 13, the x direction extends perpendicular to the component plane in which the system of the projection exposure apparatus 1 is accommodated. The coordinate system of FIGS. 4 to 11 is rotated by 90 ° around the z axis with respect to the x direction.

  FIG. 1 very schematically shows one main component of a projection exposure apparatus 1 of the system.

  The light source 2 first simulates the illumination imaging light 3 in the form of an EUV raw beam 4. FIG. 3 very schematically shows a cross-section through the EUV raw beam 4 with an x / y aspect ratio of 1: 1 on the left. Generally, the raw beam 4 exists as a beam having a Gaussian intensity distribution, that is, a beam having a circular cross section indicated by a broken line boundary 5 in FIG. The EUV raw beam 4 has a very small divergence.

であり、図３に示すように、照明光３の矩形ビームプロファイルがもたらされる。ＥＵＶ集合出力ビーム７は、均一に照明される矩形の形状を有する。このアスペクト比寄与

は、望ましい設定値アスペクト比、例えば、照明される物体視野のアスペクト比を乗じることができる。 The beam shaping optical unit 6 (see FIG. 1) functions to generate an EUV collective output beam 7 from the EUV raw beam 4. This is shown very schematically in FIG. 1 and in somewhat more detail in FIG. The EUV collective output beam 7 has a very small divergence. In FIG. 3, the aspect ratio of the EUV collective output beam 7 is designated in the second cross-sectional view from the left as before. This aspect ratio is determined in advance by the beam shaping optical unit 6 depending on the number N of the projection exposure apparatuses 1 supplied by the light source 2 in the system. The x / y aspect ratio generated by the beam shaping optical unit 6 is approximately

As shown in FIG. 3, a rectangular beam profile of the illumination light 3 is provided. The EUV collective output beam 7 has a rectangular shape that is uniformly illuminated. This aspect ratio contribution

Can be multiplied by the desired set aspect ratio, eg, the aspect ratio of the illuminated object field.

  FIG. 2 shows a system design for N = 4, so that the light source 2 supplies illumination light 3 to four projection exposure apparatuses according to the type of projection exposure apparatus 1 described in FIG. At N = 4, the x / y aspect ratio of the EUV collective output beam 7 is 2: 1. The number N of the projection exposure apparatuses 1 can be larger, for example, up to 10 units.

  In another system design, the EUV collective output beam has an x / y aspect ratio of N: 1. This ratio can also be multiplied by the desired setting aspect ratio.

The output coupling optical unit 8 (see FIGS. 1 and 2) has a plurality of EUV collective output beams 7, ie N EUV individual output beams 9 ₁ to 9 _N (i = 1,... N). ).

1 are those of exactly one of these individual output beam 9, that is, the further guidance of the output beam 9 _1. Another EUV individual output beam 9 _i , also schematically shown in FIG. 1, generated by the output coupling optical unit 8, is supplied to the other projection exposure apparatus of the system.

  Downstream of the output coupling optical unit 8, the illumination imaging light 3 is arranged by a beam guiding optical unit 10 (see FIG. 1) with a lithographic mask 12 in the form of a reticle as an object to be projected inside. Guided toward the object field 11 of the projection exposure apparatus 1. The beam shaping optical unit 6 and the output coupling optical unit 8 together with the beam guiding optical unit 10 constitute an illumination system for the projection exposure apparatus 1.

Beam guiding optical unit 10 includes the beam path for the illumination light 3, namely, in the order of the beam path for the EUV individual output beam 9 _i, an input coupling optical unit in the form of the focus assembly 14, and a downstream illumination optical unit 15 . The illumination optical unit 15 has functions corresponding to those known in the prior art, and therefore the field facet mirror 16 and the pupil facet mirror which are only very schematically illustrated in FIG. 1 without the associated EUV beam path. 17 and the like.

  After reflection at the field facet mirror 16, the used radiation beam of the illumination light 3 divided into EUV partial beams assigned to individual field facets (not shown) of the field facet mirror 16 is reflected on the pupil facet mirror 17. Is incident on. The pupil facet (not illustrated in FIG. 1) of the pupil facet mirror 17 is circular. Of these pupil facets, an incident facet pair comprising one of the field facets and one of the pupil facets predetermines an illumination channel or beam guide channel for the relevant partial beam of the used radiation beam in each case. Are assigned to each partial beam of the used radiation beam reflected from one of the field facets. The assignment of the pupil facets by channel to the field facets is performed depending on the desired illumination by the projection exposure apparatus 1. Accordingly, the illumination light 3 is guided to predetermine the individual illumination angles along the illumination channel in succession through a pair comprising a respective one of the field facets and a respective one of the pupil facets. The In order to drive each predetermined pupil facet, the field facet mirror is individually tilted in each case.

  The field facet passes through the pupil facet mirror 17 and, if appropriate, for example through the downstream transmission optical unit of three EUV mirrors (not illustrated), the projection optical unit 19 (see FIG. 1) of the projection exposure apparatus 1. Also imaged in the illumination field or object field 11 in the reticle plane or object plane 18 (also schematically shown).

  From the individual illumination angles caused through all the illumination channels by the illumination of the field facets of the field facet mirror 16, an illumination angle distribution of the illumination of the object field 11 by the illumination optical unit 15 is provided.

  In yet another embodiment of the illumination optical unit 15, the mirror of the transmission optical unit upstream of the object field 11 can be omitted, in particular assuming the appropriate position of the entrance pupil of the projection optical unit 19, so that the radiation beam used A corresponding increase in the illumination of the projection exposure apparatus 1 is caused.

  The reticle 12 that reflects the used radiation beam is arranged in the region of the object field 11 in the object plane 18. The reticle 12 is carried by a reticle holder 20 that can be displaced in a manner driven by a reticle displacement drive 21.

  The projection optical unit 19 focuses the object field 11 on the image field 22 on the image plane 23. During the projection exposure, a wafer 24 carrying the photosensitive layer exposed by the projection exposure apparatus 1 during the projection exposure is arranged in this image plane 23. The wafer 24 is in this case carried by a wafer holder 25 which can be displaced in a controlled manner using a wafer displacement drive 26.

  During projection exposure, both the reticle 12 and the wafer 24 of FIG. 1 are scanned synchronously with the x-direction by corresponding drive of the reticle displacement drive 21 and the wafer displacement drive 26. The wafer is scanned in the x direction during the projection exposure, typically at a scanning speed of 600 mm / s.

  4 and 5 show an embodiment of the beam shaping optical unit 6. The beam shaping optical unit 6 shown in FIGS. 4 and 5 has a total of four mirrors BS1, BS2, BS3, and BS4 that are sequentially numbered in the order in which the illumination light 3 enters. FIG. 4 shows the beam shaping optical unit 6 in a view parallel to the xz plane. FIG. 5 shows the beam shaping optical unit 6 in a plan view parallel to the yz plane.

  An example of beam deflection by the mirrors BS1 to BS4 of the beam shaping optical unit 6 of FIGS. 4 and 5 is shown by the mirrors MS1 and BS4 of FIG. 4 and the mirrors BS2 and BS3 of FIG. Is deviated from reality only in the plan view facing the observer. Actually, the reflecting surface of the mirror BS4 in FIG. 4 and the reflecting surface of the mirror BS3 in FIG. 5 deviate from the observer.

  The illumination light 3 is incident on the mirrors BS1 to BS4 with grazing incidence. The grazing incidence is present when the incident angle α between the main direction of incidence or reflection of the illumination light 3 and the normal N to the reflecting surface section of each mirror on which the illumination light 3 is incident is greater than 60 °. . The incident angle α can be, for example, greater than 65 °, can be greater than 70 °, and can be greater than 75 °.

The beam shaping optical unit 6 shown in FIGS. 4 and 5 comprises two beam shaping mirror groups 27, 28, that is to say a beam comprising mirrors BS 1 and BS 4, which are also initially denoted by 27 ₁ and 27 ₂ in FIG. A shaping mirror group 27 and a beam shaping mirror group 28 including mirrors BS2 and BS3, which are also denoted by 28 ₁ and 28 _{2 in} FIG. Each of the mirror groups 27 and 28 has a common group incident plane. The incident plane of the mirror group 27 is parallel to the yz plane (drawing of FIG. 5). The incident plane of the mirror group 28 is parallel to the xz plane (drawing of FIG. 4). Accordingly, the two group incidence planes yz and xz of the mirror groups 27 and 28 are different from each other and perpendicular to each other in the illustrated embodiment.

  The beam shaping mirror group 27 functions for beam shaping of the EUV collective output beam 7 in the yz plane. The beam shaping mirror group 28 functions for beam shaping of the EUV collective output beam 7 in the xz plane.

  On the other hand, the beam shaping mirror group 27 and the other 28 have the effect of a Galileo cylindrical telescope in principle. For example, to provide a reshaping of the beam profile from a substantially circular raw beam 4 having a Gaussian intensity distribution to a substantially rectangular EUV collective output beam 7 having a uniform intensity distribution in the range of the rectangular working cross section. At least some of the beam shaping mirror groups 27 and / or 28 mirrors can be provided with a free-form profile, i.e. these mirrors can have a free-form surface as a reflective surface. A free-form profile is a height distribution that cannot be represented as a cone. The cone in this case should also be understood to mean a surface shape represented by two different cones in the orthogonal direction, an example of such a surface shape being a cylinder. A free-form profile cannot be represented by such a cone. The deviation of the height distribution of one or more mirrors of the beam shaping optical unit 6 may be greater than 1 micrometer (μm), in particular greater than 5 micrometers, in particular greater than 20 micrometers. .

  The mirror group 28 including the mirrors BS2 and BS3 is generally downstream of the first mirror BS1 of the further mirror group 27 and in the beam path upstream of the second and last mirror BS4 of this further mirror group 27. Be placed.

  Based on the embodiment of the beam shaping optical unit 6, the incident angle of the illumination light 3 can be the same on all mirrors of one of the mirror groups 27, 28, or one of the mirror groups 27, 28. Can be of different sizes on at least two mirrors. In this connection, the angle of incidence should be understood to mean the angle of incidence of the ray traveling in the center in the EUV raw beam 4.

  The mirror BS1 is embodied as a convex cylindrical mirror having a cylindrical axis extending parallel to the x axis. The mirror BS2 is embodied as a convex cylindrical mirror having a cylindrical axis extending parallel to the y axis. The mirror BS3 is embodied as a concave cylindrical mirror having a cylindrical axis extending parallel to the y-axis. The mirror BS4 is embodied as a concave cylindrical mirror having a cylindrical axis extending parallel to the x axis.

  The mirror group 27 allows the beam diameter of the raw beam to be expanded on the x coordinate axis by a factor of two compared to the expansion effect of the y coordinate axis of the mirror group 28. Further, the two mirror groups 27 and 28 function to shape a rectangular cross-sectional profile of the EUV collective output beam 7.

6 to 11 show still another embodiment of the beam shaping optical unit 6. These embodiments differ in the order of deflection angles produced by the various beam shaping mirrors BS _i (i = 1,...). Therefore, in FIGS. 6 to 11, the mirror itself is not physically shown in each case, and only the deflection effect of the mirror BS _i is shown.

  Embodiment 6 of the beam shaping optical unit shown in FIG. 6 and FIG. 7 relates to the incident angle of the illumination light 3 on the mirrors BS1 to BS4 and also relates to the assignment of the mirrors BS1 to BS4 to the mirror groups 27 and 28. FIG. And corresponds to the embodiment described in FIG. The incident angle α of the illumination light 3 at the mirrors BS1 to BS4 is the same for all these mirrors in the case of the embodiment described in FIGS. Therefore, the main beam direction of the EUV collective output beam 7 is equal to the main beam direction of the EUV raw beam 4 incident on the beam shaping optical unit 6.

  8 and 9 show yet another embodiment 29 of a beam shaping optical unit that can be used in place of the beam shaping optical unit 6 described in FIGS. Components and functions corresponding to those described above with reference to the beam shaping optical unit 6 are accompanied by the same reference numerals in the case of the beam shaping optical unit 29 and will not be described in detail again.

  In contrast to the beam shaping optical unit 6, in the case of the beam shaping optical unit 29, there are different incidence angles α, β of EUV radiation on the mirrors BS1 to BS4. In each case, the mirrors BS1 and BS2 reflect the beam path of the beam shaping optical unit 29 up to the third mirror BS3 at an incident angle α so as to correspond to the beam path in the beam shaping optical unit 6. In the mirrors BS3 and BS4, the illumination light 3 is reflected with a grazing incidence although it has an incident angle β smaller than the incident angle α. This reflection is such that the main beam direction of the EUV collective output beam 7 emitted from the beam shaping optical unit 29 does not extend in parallel with the z direction, and in both the xz plane and the yz plane, the incident direction extends in parallel with the z direction. This has the effect of forming an angle different from zero.

  The smaller angle of incidence β in the last two mirrors BS3 and BS4 of the beam shaping optical unit 29 has a structurally smaller embodiment of these last two mirrors BS3 and BS4, ie a smaller spreading reflective surface. Allows embodiments. In this embodiment, at the location of these last mirrors BS3 and BS4, the illumination light is already considerably enlarged in cross-section compared to the incident EUV raw beam, so that beam shaping is better than the two leading mirrors BS1 and BS2. It has a greater significance for these last two mirrors BS3 and BS4 of the optical unit 29.

  10 and 11 show yet another embodiment 30 of a beam shaping optical unit that can be used in place of the beam shaping optical units 6, 29. Components and functions corresponding to those described above with reference to the beam shaping optical units 6 and 29 are accompanied by the same reference numerals in the case of the beam shaping optical unit 30 and will not be described in detail again. .

  The beam shaping optical unit 30 has a total of five mirrors BS1, BS2, BS3, BS4, BS5 that are sequentially numbered in the order in which the illumination light 3 is incident as before. The mirrors BS1, BS2 and BS5 belong to the first mirror group 27 of the beam shaping optical unit 30 having a yz incidence plane. The remaining two mirrors BS3 and BS4 belong to the mirror group 28 having an xz incident plane.

  After reflection at the first mirror BS1, the beam path of the illumination light 3 in the beam shaping optical unit 30 corresponds to that in the beam shaping optical unit 29, in this case from the mirror BS2 of the beam shaping optical unit 30. BS5 has the functions of mirrors BS1 to BS4 of the beam shaping optical unit 29.

  The illumination light 3, that is, the EUV raw beam 4 is incident on the first BS 1 of the beam shaping optical unit 30 with strong grazing incidence. Therefore, the incident angle γ of the illumination light 3 on the first BS 1 of the beam shaping optical unit 30 is larger than the incident angle α. The incident angle γ accurately compensates for the beam direction difference of the illumination light 3 in the yz plane that appears on the one hand between the mirrors BS1 and BS2 and on the other hand downstream of the mirror BS5 by the illumination light 3, thereby providing a beam shaping optical unit. The main beam direction of the illumination light 3 in the yz plane after exiting from 30 is parallel to the main beam direction in the yz plane at the time of incidence on the beam shaping optical unit 30, that is, parallel to the z direction. Have a large size.

  Upstream and downstream of the beam shaping optical unit 30, the illumination light 3 travels parallel to the ceiling of the building that includes the system inside.

Group incidence of the mirror group 27 of the beam shaping optical unit 30 in which the individual mirrors 27 ₁ (BS1), 27 ₂ (BS2) and 27 ₃ (BS5) have different angles of incidence, ie, γ, α and β inside. When projected onto the plane yz, the EUV collective output beam 7 generated by the beam shaping optical unit 30 travels in the same direction as the EUV raw beam 4 incident on the beam shaping optical unit 30, that is, the z direction.

  Typical cross-sectional dimensions of the reflecting surfaces of the last mirrors BS4 and BS5 of the beam shaping optical units 6 and 30 are 1 m to 1.5 m, respectively, and these mirrors are generally rectangular as a first approximation. Has a face and the specified cross-sectional dimension is for the longer of the two axes. The typical cross-sectional dimension of the reflecting surface of the first mirror BS1 of the beam shaping optical unit is 20 mm to 100 mm.

  After exiting the beam shaping optical unit 6 or 30, the rays of the EUV collective output beam 7 travel substantially parallel. The divergence of the EUV collective output beam 7 can be smaller than 10 mrad, in particular smaller than 1 mrad, in particular smaller than 100 μrad, in particular smaller than 10 μrad.

FIGS. 2 and 12 show an example of the output coupling optical unit 8 for generating the EUV individual output beam 9 from the EUV collective output beam 7. The output coupling optical unit includes EUV individual output beams 9 ₁ , 9 ₂ ,. . . , And a plurality of output coupling mirrors 31 ₁ , 31 ₂ ,. . . Have FIG. 2 shows the arrangement of the output coupling mirror 31 such that the illumination light 3 is deflected by 90 ° by the output coupling mirror 31 during decoupling. An embodiment in which the output coupling mirror 31 is actuated using grazing incidence of the illumination light 3 as schematically shown in FIG. In the embodiment described in FIG. 2, the incident angle α of the illumination light 3 on the output coupling mirror 31 is about 70 °, but it can even be significantly exceeded, and the EUV by each output coupling mirror 31. The effective deflection of the individual output beam 9 can be, for example, in the region of 85 ° so that it is 10 ° compared to the direction of incidence of the EUV collective output beam 7.

Each of the output coupling mirrors 31 _i is thermally coupled to a heat sink (not illustrated in detail).

FIG. 2 has a total of four output coupling mirrors 31 ₁ to 31 ₄ . FIG. 12 shows a modification of the output coupling optical unit 8 having a total of three output coupling mirrors 31 ₁ to 31 ₃ . Different numbers N of output coupling mirrors 31 are possible depending on the number N of projection exposure apparatuses 1 supplied by the light source 2, for example N = 2 or N ≧ 4, in particular N ≧ 8.

のｘ／ｙアスペクト比を有する。図３の右から第２の断面図は、このアスペクト比を有するＥＵＶ個別出力ビーム９のうちの１つを示している。従って、Ｎ＝４の場合に、ｘ／ｙアスペクト比は１：２である。このアスペクト比寄与にも、望ましい設定値アスペクト比を乗じることができる。 After decoupling, each of the EUV individual output beams 9 is

X / y aspect ratio. The second cross-sectional view from the right in FIG. 3 shows one of the EUV individual output beams 9 having this aspect ratio. Therefore, when N = 4, the x / y aspect ratio is 1: 2. This aspect ratio contribution can also be multiplied by the desired set value aspect ratio.

The output coupling mirrors 31 _i (i = 1, 2,...) Are such that each closest output coupling mirror 31 _i reflects a marginal cross-section portion of the EUV collective output beam 7 so that this cross-section portion is The remaining EUV collective output beam 7 passing by the output coupling mirror 31i is decoupled in the beam path of the EUV collective output beam 7 in the beam direction of the EUV collective output beam 7 so as to be decoupled. This output coupling from the edge is followed by subsequent output coupling mirrors 31 _i +1,... Until the last cross-section portion that remains despite that of the EUV collective output beam 7 is decoupled. . . Repeated by.

In the cross section of the EUV collective output beam 7, it is assigned to the EUV individual output beam 9 _i on a separation line 32 extending parallel to the y-axis, ie, parallel to the short side of the x / y rectangular cross section of the EUV collective output beam 7. Separation between the created cross-sectional parts is performed. The separation of the EUV individual output beam 9 _i is carried out in such a way that in each case the cross-sectional part furthest from the next optical component in the beam path is cut off. This facilitates cooling of the output coupling optical unit 8 in particular.

  The deflection optical unit 13 downstream of the output coupling optical unit 8 in the beam path of the illumination light 3 firstly ensures that the EUV individual output beam 9 has a vertical beam direction downstream of this deflection optical unit 13 in each case. Secondly, in order to deflect the EUV individual output beam 9, it functions to adapt the x / y aspect ratio of the EUV individual output beam 9 to a 1: 1 x / y aspect ratio as shown at the right end of FIG. 3. To do. This aspect ratio contribution can also be multiplied by the desired set value aspect ratio. Thus, the above x / y aspect ratio is an aspect ratio contribution that is multiplied by a setpoint aspect ratio, eg, the aspect ratio of a rectangular or arcuate object field, to yield the desired actual aspect ratio. The above-mentioned x / y set value aspect ratio can be the aspect ratio of the first optical element of the illumination optical unit 15. The x / y set value aspect ratio described above can be the aspect ratio of the angle of the illumination light 3 at the intermediate focus 42 of the illumination optical unit 15.

  When the vertical beam path of the EUV individual output beam 9 already exists downstream of the output coupling optical unit 8, the deflection effect of the deflection optical unit 13 can be omitted, and the adaptation of the EUV individual output beam 9 with respect to the x / y aspect ratio. The effect is sufficient.

The EUV individual output beam 9 downstream of the deflecting optical unit 13 enters the illumination optical unit 15 at an angle that allows efficient folding of the illumination optical unit after passing through the focus assembly 14 if appropriate. You can go forward. Downstream of the deflecting optical unit 13, the EUV individual output beam 9 _i is from 0 ° to 10 ° to the vertical, from 10 ° to 20 ° to the vertical, or from 20 ° to the vertical. You can proceed at angles up to 30 °.

  In the following, various modifications relating to the deflection optical unit 13 will be described with reference to FIGS. In this case, the illumination light 3 is schematically shown as a single light beam, that is, the illustration of the beam is omitted.

The divergence of the EUV individual output beam 9 _i after passing through the deflecting optical unit is less than 10 mrad, in particular less than 1 mrad, in particular less than 100 μrad, ie any 2 in the beam of the EUV individual output beam 9 _i The angle between the two rays is less than 20 mrad, in particular less than 2 mrad, in particular less than 200 μrad. This is satisfied for the variants described below.

  The deflecting optical unit 13 shown in FIG. 13 deflects the decoupled EUV individual output beam 9 as a whole with a deflection angle of about 75 °. Accordingly, the EUV individual output beam 9 is incident on the deflecting optical unit 13 shown in FIG. 13 at an angle of about 15 ° with respect to the horizontal (xy plane), and the deflecting optical unit 13 is parallel to the x axis of FIG. Eject in a proper beam direction. The deflection optical unit 13 has a total transmission rate of about 55% for the EUV individual output beam 9.

  The deflection optical unit 13 shown in FIG. 13 has a total of six deflection mirrors D1, D2, D3, D4, D5, and D6 that are sequentially numbered in the order in which the illumination light 3 enters in the beam path. From the deflecting mirrors D1 to D6, only one section passing through these reflecting surfaces in each case is shown schematically, and the curvature of each reflecting surface is significantly exaggerated. The illumination light 3 is incident on the all of the mirrors D1 to D6 of the deflection optical unit 13 shown in FIG. 13 with grazing incidence in a common deflection incidence plane parallel to the xz plane.

  The mirrors D1 and D2 are embodied as convex cylindrical mirrors having a cylindrical axis parallel to the y axis. The mirror D3 is embodied as a plane mirror. The mirrors D4 to D6 are again embodied as concave cylindrical mirrors having a cylindrical axis parallel to the y-axis.

  A convex cylindrical mirror is also called a dome-shaped mirror. A concave cylindrical mirror is also called a dish-shaped mirror.

から値１：１に適応されるようなものである。従って、この比におけるｘ寸法において、ビーム断面が

倍だけ伸ばされる。 The combined beam shaping effect of mirrors D1 to D6 is the x / y aspect ratio

To the value 1: 1. Thus, for the x dimension at this ratio, the beam cross section is

Only doubled.

  At least one of the deflection mirrors D1 to D6, or else all of the deflection mirrors D1 to D6, can be embodied as displaceable in the x and / or z direction using the assigning actuator 34. As a result, the deflection optical unit 13 can be adapted to adapt the deflection effect first and the aspect ratio adaptation effect second. Alternatively or additionally, at least one of the deflection mirrors D1 to D6 can be embodied as a mirror that is adaptable with respect to its radius of curvature. For this purpose, each mirror D1 to D6 can be composed of a plurality of individual mirrors that can be displaced relative to each other by an actuator system not illustrated in this figure.

The various optical assemblies of the system including the projection exposure apparatus 1 can be implemented adaptively. Accordingly, the EUV individual output beam 9 _i from the light source 2 is intended to be supplied to the projection exposure apparatus 1 and the individual EUV individual outputs after passing through the respective deflection optical units 13. What energy ratio and what beam geometry is intended to exist for the beam 9 can be centrally predetermined. Based on the predetermined value, the EUV individual output beam 9 _i can vary in its intensity and its set value x / y aspect ratio. In particular, the energy ratio of the EUV individual output beam 9 _i can be changed by setting the output coupling mirror 31 _i to be adaptive, and the deflection optical unit 13 can be changed by setting the deflection optical unit 13 to be adaptive. Thereafter, the size and aspect ratio of the EUV individual output beam 9 _i can be kept unchanged.

  Still another embodiment of a deflection optical unit that can be used in place of the deflection optical unit 13 shown in FIG. 13 in a system including N projection exposure apparatuses 1 will be described below with reference to FIGS. explain. The components and functions described above with reference to FIGS. 1 through 13, and in particular with reference to FIG. 13, carry the same reference numerals and will not be described again in detail.

  The deflection optical unit 35 described in FIG. 14 has a total of four mirrors D1, D2, D3, D4 in the beam path of the illumination light 3. The mirror D1 is embodied as a convex cylindrical mirror. The mirrors D2 to D4 are embodied as concave cylindrical mirrors.

図１４に関する表 More detailed optical data can be achieved from the table below. In this case, the first column represents the radius of curvature of each mirror D1 to D4, and the second column represents the distance between each mirror D1 to D3 and each subsequent mirror D2 to D4. Yes. This distance relates to the distance traveled by the central ray in the EUV individual output beam 9 _i between the corresponding reflections. Units used in this and subsequent tables are mm in each case unless otherwise stated. In this case, the EUV individual output beam 9 _i is incident on the deflection optical unit 13 using a half diameter d _in 2 of 10 mm.

Table related to FIG.

  The deflection optical unit 35 shown in FIG. 14 enlarges the x / y aspect ratio by a factor of three.

  FIG. 15 shows a further embodiment 36 of the deflection optical unit which also includes four mirrors D1 to D4. The mirror D1 is a convex cylindrical mirror. The mirror D2 is a plane mirror. The mirrors D3 and D4 are two cylindrical mirrors having the same radius of curvature.

図１５に関する表 More detailed optical data can be achieved from the table below corresponding to the table for FIG.

Table for FIG.

  The deflection optical unit 35 shown in FIG. 15 expands the x / y aspect ratio of the EUV individual output beam 9 twice.

  FIG. 16 shows a further embodiment 37 of the deflection optical unit comprising five mirrors D1 to D5. The first mirror D1 is a convex cylindrical mirror. The second mirror D2 is a plane mirror. Further mirrors D3 to D5 are three concave cylindrical mirrors.

図１６に関する表 More detailed data can be achieved with respect to the layout from the following table corresponding to the tables for FIGS.

Table for FIG.

  The deflection optical unit 37 shown in FIG. 16 expands the x / y aspect ratio of the EUV individual output beam 9 by 5 times.

表「図１６に関する代替設計」 Yet another embodiment of the deflection optical unit 37 differs from the embodiment described in FIG. 16 only in the radius of curvature and mirror distance shown in the table below.

Table "Alternative Design for Figure 16"

  In contrast to the first embodiment described in FIG. 16, this alternative design has a magnification factor of 4 with respect to the x / y aspect ratio.

図１６に関する表「更に別の代替設計」 Yet another embodiment 37 of the deflection optical unit differs from the embodiment described in FIG. 16 in the radius of curvature and mirror distance shown in the table below.

Table “Further Alternative Design” for FIG.

  In contrast to the embodiment described above, this further alternative design has a magnification factor of 3 with respect to the x / y aspect ratio. The last two mirrors D4 and D5 have the same radius of curvature.

  FIG. 17 shows a further embodiment of the deflection optical unit 38 comprising six mirrors D1 to D6. The first mirror D1 is a convex cylindrical mirror. The next two deflection mirrors D2 and D3 are concave cylindrical mirrors having the same radius of curvature in each case. The next deflection mirror D4 is a plane mirror. The last two deflection mirrors D5 and D6 of the deflection optical unit 38 are concave cylindrical mirrors having the same radius of curvature again.

図１７に関する表 More detailed data can be achieved from the following table corresponding to the table for FIG.

Table for FIG.

  The deflection optical unit 38 has a magnification factor of 5 with respect to the x / y aspect ratio.

  FIG. 18 shows a further embodiment 39 of the deflection optical unit comprising six mirrors D1 to D6. The first mirror D1 of the deflection optical unit 39 is a convex cylindrical mirror. The second deflection mirror D2 located downstream is a plane mirror. The downstream deflection mirrors D3 to D6 are concave cylindrical mirrors in each case. On the one hand, the radii of curvature of the mirrors D3 and D4 and on the other hand the radii of curvature of the mirrors D5 and D6 are equal.

図１８に関する表 More detailed data can be achieved with respect to the layout from the following table corresponding to the table for FIG.

Table for FIG.

  The deflection optical unit 39 has an enlargement factor of 5 with respect to the x / y aspect ratio.

表「図１８に関する代替設計」 In an alternative design with respect to FIG. 18, the convex / planar / concave / concave / concave / concave mirror order is exactly the same as in the embodiment of the deflection optical unit 39 described above. This alternative design for FIG. 18 differs in the specific radius of curvature and mirror distance, as illustrated by the following table.

Table "Alternative Design for Figure 18"

  This alternative design for FIG. 18 has a magnification factor of 4 with respect to the x / y aspect ratio of the EUV individual output beam 9.

  FIG. 19 shows a further embodiment 40 of the deflection optical unit comprising six mirrors D1 to D6. The first deflection mirror D1 of the deflection optical unit 40 is a convex cylindrical mirror. The two downstream deflection mirrors D2 and D3 are plane mirrors. The downstream deflection mirrors D4 to D6 of the deflection optical unit 40 are concave cylindrical mirrors. The last two deflection mirrors D5 and D6 have the same radius of curvature.

図１９に関する表 More detailed data can be achieved from the following table corresponding to the table for FIG.

Table for FIG.

  The deflection optical unit 40 has a magnification factor of 5 with respect to the x / y aspect ratio.

  In yet another variant (not illustrated), the deflection optical unit has a total of eight mirrors D1 to D8. The two leading deflection mirrors D1 and D2 in the beam path of the EUV individual output beam 9 are concave cylindrical mirrors. The four downstream deflection mirrors D3 to D6 are convex cylindrical mirrors. The last two deflection mirrors D7 and D8 of this deflection optical unit are again concave cylindrical mirrors.

  These mirrors D1 to D8 are connected to the actuator 34 in the same manner as the mirror D1 of FIG. 13, and the distance between the adjacent mirrors D1 to D8 can be determined in advance by these actuators.

The following table shows the design of this deflecting optical unit including eight mirrors D1 to D8, in addition to the radius of curvature, the mirror distances for various half diameters d _out / 2 of the exit EUV individual output beam 9 _i are also shown. Show. In this case, the EUV individual output beam enters the deflection optical unit including the eight mirrors D1 to D8 with a half diameter d _in / 2 of 10 mm, and receives the EUV individual subjected to deflection based on the distance value shown in the figure. It provides magnifications of 4.0, 4.5, and 5.0 with respect to the x / y aspect ratio of the output beam 9 _i .

In yet another embodiment of the deflection optical unit (also not illustrated), there are four mirrors D1 to D4. The first mirror D1 and the third mirror D3 in the beam path of the EUV individual output beam 9 _i are embodied as concave cylindrical mirrors. The following table shows the distance values calculated for the input half diameter d _in / 2 of the 10 mm EUV individual output beam 9 _i in addition to the radius of curvature, ie when passing through this deflection group including four mirrors D1 to D4. Magnification factors of 1.5 (half diameter d _out / 2 15 mm), 1.75 (half diameter d _out / 2 17.5 mm), and 2.0 (half diameter d _out / 2 20 mm) for the x / y aspect ratio The distance value that yields is also shown.

The deflection optical unit 13 can be designed such that parallel incident light exits the deflection optical unit again in parallel. The deviation angle in the light beam direction of the EUV individual output beam 9 _i incident on the deflecting optical unit 13 at parallel incidence is smaller than 10 mrad, particularly smaller than 1 mrad, especially smaller than 100 μrad after exiting the deflecting optical unit. be able to.

  The mirror Di of the deflecting optical unit 13 can be embodied so as not to have refractive power, that is, in a planar manner. In the realization in this plane method, particularly when N is the number of projection exposure apparatuses 1 supplied by the light source 2, the x / y aspect ratio of the EUV collective output beam 7 has an aspect ratio of N: 1. Yes, if you have it. This aspect ratio can be multiplied by a desired set value aspect ratio.

  The deflecting optical unit 13 of the mirror Di having no refractive power can be composed of 3 to 10 mirrors, in particular 4 to 8 mirrors, in particular 4 or 5 mirrors.

  The light source 2 can emit linearly polarized light, and the polarization direction of the illumination light 3 when entering the mirror of the deflecting optical unit 13, that is, the direction of the electric field intensity vector, is perpendicular to the incident plane. be able to. The deflecting optical unit 13 of the mirror Di having no refractive power can be composed of fewer than three mirrors, in particular one mirror.

  In the beam guiding optical unit 10, a focus assembly 41, which is also referred to as an input coupling optical unit, is disposed downstream of each deflection optical unit in the beam path of each EUV individual output beam 9.

FIG. 20 schematically shows the function of the input coupling optical unit 41 for one of the EUV individual output beams 9 _i . The focus assembly 41 transmits each EUV individual output beam 9 _i to the intermediate focus 42 of the beam guiding optical unit 10. The intermediate focus 42 is disposed at the position of the through opening 43 for the illumination light 3. The through opening 43 can be embodied on the ceiling of a building in which the system including the projection exposure apparatus 1 is included. The ceiling extends in the intermediate focal plane 44 of the beam guiding optical unit 10 also shown in FIG.

  The focus assembly 41 has an effective deflection angle of about 10 ° with respect to the central chief ray CR.

  In another configuration, the focus assembly 41 has an effective deflection angle between δ / 2 and δ with respect to the central chief ray CR when δ is the angle between the central chief ray and the peripheral ray at the intermediate focus 42. . The sine value of δ is also referred to as the numerical aperture (NA) of the radiation 3 at the intermediate focus 42.

FIG. 21 illustrates the focus effect of an alternative focus assembly 45 that can be used in place of the focus assembly 41 described in FIG. In contrast to the focus assembly 41, the focus assembly 45 is incident EUV individual output beam 9 All the same polarization direction of the individual rays in xz incidence plane of the _i, namely, to deflect toward the negative y values. The minimum deflection angle of the focused individual ray 46 of the EUV individual output beam 9 _i shown at the left end of FIG. 21 is denoted by α in FIG. 21, and α is 5 ° or smaller.

  The focus assembly 45 has an effective deflection angle of about 20 ° with respect to the central chief ray CR.

  In another configuration, the focus assembly 45 has an effective deflection angle between δ / 2 and δ with respect to the central chief ray CR when δ is the angle between the central chief ray and the peripheral ray at the intermediate focus 42. .

  An embodiment variant relating to the focus assembly that can be used for the focus assembly 41 or 45 is described below with reference to FIGS.

  22 to 25 show meridional sections through the mirror reflection surfaces involved in each case. Use reflection portions of these mirror surfaces are highlighted with bold lines. In order to explain the elliptical hyperboloid / parabolic surface design for the shape characteristics of each mirror, the notch of the base material surface is also drawn with thin lines.

The focus assembly 46 shown in FIG. 22 has two mirrors arranged downstream in the beam path of each EUV individual output beam 9 _i , that is, a leading ellipsoidal mirror 47 and a downstream hyperboloidal mirror 48. .

In the case of the focus assembly 46, the effective deflection angle of the EUV individual output beam 9 _i with respect to the central principal ray CR is about 50 °. In the case of the focus assembly 46, the deflection angles with respect to the central principal ray CR when reflected by the two mirrors 47 and 48 are added.

  The mirrors 47 and 48 are embodied as concave mirrors. The focus assembly 46 is embodied in the form of a type I Walter collector. Information on various types of Walter collectors can be found in H.C. Wolter, “Spigelsystems Eiffens als abbilende Optiken fur Rongenstrahlen”, Vol. 10, p. 94, p. 114, p. 114.

In an alternative configuration, the effective deflection angle of the EUV output beam 9 _i with respect to the central principal ray CR in the case of the focus assembly 46 is less than 40 °, in particular less than 30 °, in particular less than 15 °, in particular more than 10 °. Is also small.

In an alternative configuration, the effective deflection angle of the EUV output beam 9 _i with respect to the central chief ray CR for the focus assembly 46 is less than twice the angle between the central chief ray CR and the peripheral ray at the intermediate focus 42.

  Similarly, the focus assembly 49 shown in FIG. 23 includes two mirrors, that is, a leading ellipsoidal mirror 50 and a downstream hyperboloidal mirror 51.

  The mirror 50 is concave, and the mirror 51 is convex.

  In the case of the focus assembly 49, the deflection angle with respect to the central principal ray CR when reflected by the mirrors 50 and 51 is subtracted.

  In the case of the focus assembly 49, the effective deflection angle with respect to the chief ray CR is about 30 °.

  The focus assembly 49 is embodied in a type II Walter collector scheme.

  In an alternative configuration, the focus assembly 49 has an effective deflection angle of at most 20 °, in particular at most 15 °, in particular at most 10 ° with respect to the principal ray CR.

  In one configuration of the focus assembly 49, the effective deflection angle for the chief ray CR is less than twice the angle between the chief ray CR and the peripheral ray at the intermediate focus 42.

The focus assembly 52 shown in FIG. 24 also has two mirrors arranged along the path flow in the beam path of the EUV individual output beam 9 _i , namely a leading parabolic mirror 53 and a downstream ellipsoidal mirror 54. And have.

  The mirror 53 is convex, and the mirror 54 is concave.

  In the case of the focus assembly 52, the deflection angle with respect to the central principal ray CR when reflected by the mirrors 53 and 54 is subtracted.

  In the case of the focus assembly 52, the effective deflection angle with respect to the chief ray CR is about 50 °.

  The focus assembly 52 is embodied in a type III Walter collector scheme.

  FIG. 25 shows yet another embodiment 52 of the focus assembly that is also embodied in a type III Walter collector scheme. The components and functions described above with reference to the focus assembly described in FIGS. 21-24, in particular the focus assembly described in FIG. 24, carry the same reference numerals and will not be described in detail again.

The output divergence of EUV individual output beam 9 _i is predetermined by the numerical aperture NA of the EUV individual output beam 9 _i in the intermediate focus 42. Based on the numerical aperture NA, the following expression can be approximately specified for the transmission rate T of the focus assembly shown in FIG.
T = 1-0.9NA

  In this case, the numerical aperture NA is determined as a sine value of the angle between the principal ray and the peripheral ray at the intermediate focus 42. An equivalent definition explains that NA is a sine value of half the beam divergence.

  The major axis of the ellipsoid describing the reflecting surface of the ellipsoidal mirror 54 has a length a. The structural space 2a required for the focus assembly 55 has a typical dimension of 2a.

A typical structural space dimension 2 a is about 50 times the beam diameter d of the EUV individual output beam 9 _i when incident into the focus assembly 55. This ratio depends only very weakly on the numerical aperture NA at the intermediate focus 42.

  The typical dimension of the reflecting surface of the ellipsoidal mirror 54 is also a. Given a typical spread of 1.4 m of the reflecting surface of the ellipsoidal mirror 54, a diameter of about 60 mm follows for the beam diameter d.

The ellipsoidal mirror 54 has a short semi-axis b. The short half axis b is perpendicular to the drawing of FIG. The following equation holds for the half-axis ratio b / a.
b / a-0.8NA

  In this case, NA is the numerical aperture at the intermediate focus 42.

The parabolic mirror 52 has a focal length f. The following equation holds for the ratio between the major axis a of the ellipsoidal mirror 54 and the focal length f of the parabolic mirror.
a / f> 50

  During the generation of a fine or nanostructured component using the projection exposure apparatus 1, the reticle 12 and the wafer 24 are initially provided. Thereafter, the structure on the reticle 12 is projected onto the photosensitive layer of the wafer 24 using the projection exposure apparatus 1. Development of the photosensitive layer creates microstructures or nanostructures on the wafer 24, thus creating semiconductor components in the form of fine or nanostructured components, eg, memory chips.

  In the following, still another aspect of the projection exposure apparatus 1, particularly still another aspect of the beam shaping optical unit 6 will be described.

In general, the beam shaping optical unit 6 functions to form a collective output beam 7, also called a carrier beam, from the raw beam 4. The collective output beam 7 is divided into EUV individual output beams 9 _i guided to various scanners by an output coupling optical unit 8.

  The carrier beam can be easily carried over a large distance. For this purpose, it is advantageous if the carrier beam has a very small divergence. The very small divergence is advantageous in that the distance between the beam shaping optical unit 6 and the scanner, in particular the illumination optical unit 15 of the scanner, is not always known.

  In order to make it easier to split the carrier beam along the scanner, it is better for the carrier beam to have a substantially uniform intensity distribution rather than a Gaussian distribution as is customary for the raw beam 4. It is advantageous. This uniform intensity distribution can be achieved by the beam shaping optical unit 6 as described above, particularly using reflection on a free-form surface.

The collective output beam 7 having a uniform intensity distribution makes it easy to split this beam into various individual output beams 9 _i . However, it has been recognized by the present invention that uniformity requirements are not absolutely necessary to achieve dose stability for individual scanners. Furthermore, it has been recognized that the collective output beam 7 does not necessarily have a rectangular intensity distribution.

  According to one variant, the beam shaping optical unit 6 includes a mirror having a reflective surface that is not embodied as a free-form surface. In particular, the beam shaping optical unit 6 can be embodied to include only a mirror having a reflective surface that is not embodied as a free-form surface.

  In particular, the output coupling optical unit 8 and the deflection optical unit 13 include only a mirror on which the illumination light 3 is incident with a grazing incidence. The deflection of the illuminating radiation 3 with a generally desired deflection angle is caused in particular by a plurality of reflections. The total number of reflections in the output coupling optical unit 8 and the deflection optical unit 13 is in particular at least 2 times, in particular at least 3 times, in particular at least 4 times.

The beam shaping optical unit 6 is arranged between the radiation source 2 and the output coupling optical unit 8, i.e. the optical components used to split the collective output beam 7 into individual output beams _9i .

  The beam shaping optical unit 6 is embodied in particular such that the raw beam 4 is expanded in at least one direction perpendicular to the propagation direction. The beam shaping optical unit 6 is in particular embodied in such a way that the cross section of the raw beam 4 is expanded in at least one direction, in particular in two directions extending obliquely relative to each other, in particular perpendicularly. The magnification scale is preferably in the range between 1: 4 and 1:50, in particular at least 1: 6, in particular at least 1: 8, in particular at least 1:10.

  At the input of the beam shaping optical unit 6, the raw beam 4 has a cross-section with a diameter in the range of 1 mm to 10 mm in particular. At the output of the beam shaping optical unit 6, the collective output beam 7 has a diameter in particular in the range from 15 mm to 300 mm, in particular at least 30 mm, in particular at least 50 mm.

  At the input of the beam shaping optical unit 6, the raw beam 4 has a divergence, in particular in the range from 25 μrad to 100 μrad. At the output of the beam shaping optical unit 6, the divergence of the collective output beam 7 is in particular smaller than 10 μrad.

  The beam shaping optical unit 6 is particularly telecentric. The beam shaping optical unit 6 includes at least two optically effective surfaces. The optically effective surface is preferably operated with grazing incidence.

Preferably, the raw beam 4 is expanded in two directions that are oblique with respect to each other, in particular perpendicular. In this case, the beam shaping optical unit 6 comprises at least two groups with in each case at least two optically effective surfaces, in particular at least four optically effective surfaces. The beam shaping optical unit 6 includes in particular mirror groups 27 and 28. The mirror groups 27, 28 include in particular in each case two mirrors 27 _i , 28 _i .

The beam shaping optical unit 6 comprises in particular at least one beam shaping mirror group 27, 28 with in each case at least two mirrors 27 _i , 28 _i . The mirrors 27 _i , 28 _i can have a surface profile that is constant along a local coordinate in each case and has a spherical transition along a coordinate orthogonal to this coordinate. This causes an expansion of the raw beam 4 only in a single direction. Two mirror groups 27, 28 of this kind can be used to expand the raw beam 4 in two different directions, in particular two orthogonal directions.

The mirrors 27 _i , 28 _i can have a spherical transition with a radius of curvature R ₁ along the first local coordinate and a radius of curvature R ₂ along a coordinate orthogonal to this coordinate. . In this case, R ₁ and R ₂ can be equal or different. Such a deformation results in the expansion of the raw beam 4 in two mutually perpendicular directions.

The mirrors 27 _i , 28 _i can have a surface profile corresponding to an elliptical surface in each case. This also causes expansion in two directions.

  Preferably, the beam shaping optical unit 6 is arranged and embodied in such a way that the raw beam, in particular its cross section, is enlarged with respect to a direction extending parallel to the installation surface, ie parallel to the horizontal direction. The beam shaping optical unit 6 is embodied in particular such that the collective output beam 7 at the output of the beam shaping optical unit 6 extends parallel to the installation surface.

  In the following, further aspects and modifications of the beam shaping optical unit 6 will be briefly summarized and described.

  As described above, it is not absolutely necessary to make the raw beam 4 uniform by using the beam shaping optical unit 6. However, homogenization of the raw beam 4 may be advantageous. This homogenization can lead to a particularly high material life. This homogenization may also simplify the possibility of producing the output coupling optical unit 8 in particular.

  Based on which aspects are of primary importance, it may be preferable to make the raw beam 4 uniform in only one direction, which can be possible. In this respect, the homogenization of the raw beam 4 in one direction has an advantageous effect on the material life, whereas the homogenization in the direction perpendicular to this direction can be produced in particular for the output coupling optical unit 8. It has been recognized that it is advantageous for sex.

As mentioned above, the beam shaping optical unit 6 has a separate group 27, 28, in particular a separate pair of mirrors 27 _i , 28 _i in each case in these two directions, so that, for example, One can be embodied as a torus and the other as a free-form surface. This results in cost savings.

  Various variations of the homogenization of the raw beam 4 using the beam shaping optical unit 6 are shown schematically in FIGS. FIG. 26 schematically illustrates an embodiment of a beam shaping optical unit 6 that is used to homogenize the raw beam 4 in two mutually perpendicular directions. This homogenization becomes apparent from the stepwise transition of the intensity profile 56 in the first direction and the stepwise transition of the intensity profile 57 in the second direction. The intensity profiles 56, 57 relate to the intensity of the illuminating radiation 3 in the cross section of this beam perpendicular to the propagation direction of the collective output beam 7.

  FIG. 27 shows a modification of the beam shaping optical unit 6 in which the raw beam 4 is made uniform only in the second direction. Accordingly, the intensity profile 57 has a step transition. The intensity profile 56 is non-uniform, has no particular steps, and has a particularly Gaussian transition. In other words, an increase in local intensity occurs in the central region of the collective output beam 7 traveling in the vertical direction in FIG.

  FIG. 28 correspondingly illustrates a modification of the beam shaping optical unit 6 in which the raw beam 4 is precisely equalized in the other direction compared to the embodiment described in FIG. In this embodiment, the intensity profile 56 in the first direction has a step transition. The intensity profile 57 in the second direction is not uniform, has no particular steps, and is particularly Gaussian. The intensity increases in a central region that extends horizontally.

  Intermediate steps are also possible. In particular, the raw beam 4 can be partially uniformized in one or both directions. In particular, the raw beam 4 can be made uniform in one or both directions such that the intensity of the illuminating radiation in various spatial coordinates in that direction differs by at most 25% in each case. Corresponding homogenization makes it possible in particular to avoid a sudden increase in strength. Avoiding this sudden increase has a particularly advantageous effect on the material life.

  The intensity profile 56 and / or the intensity profile 57 is not particularly precisely Gaussian, not exactly stepped, and can have a form with Gaussian and stepped portions. The intensity profile 56 and / or the intensity profile 57 can be described as the sum of a Gaussian portion and a stepped portion.

The non-uniformity of the collective output beam 7 in the second direction is compensated by the fact that the area of the collective output beam 7 decoupled by the output coupling optical unit 8 into the various individual output beams 9 _i is of various sizes. can do. The size of these areas makes it possible to predetermine how much of the illumination radiation 3 in the collective output beam 7 is guided to the individual scanners.

  FIG. 29 shows an optical element for enlarging the cross section of a beam with illumination radiation 3. A mirror 58 having a convex reflecting surface is arranged in the beam path of the illumination radiation 3 in order to enlarge the beam cross section. The mirror 58 is also called a diverging mirror.

  The mirror 58 can have a substantially cylindrical reflective surface, that is, convex in the first direction and planar in a second direction extending perpendicular to the first direction. The mirror 58 can be convex in both directions. In this case, the radii of curvature can be equal or different. In principle, the mirror 58 can be embodied with an adjustable radius of curvature, in particular with an adjustable radius of curvature by the actuator system. The selection of the radius of curvature of the mirror 58 with respect to the first direction and the second direction perpendicular to this direction makes it possible to influence the enlargement of the cross-section in the corresponding direction in a targeted manner.

  The mirror 58 can be used in this way towards a targeted enlargement of the beam with illumination radiation 3 or the cross section of the light beam.

DESCRIPTION OF SYMBOLS 1 Projection exposure apparatus 2 Synchrotron radiation based light source 4 EUV raw beam 8 Output coupling | bonding optical unit 10 Beam guidance optical unit

  According to the invention, these objects are achieved by a deflecting optical unit having the features of claim 1, a beam guiding optical unit having the features of claim 9, a beam shaping optical unit having the features of claim 4, And an illumination system having the features of claim 11.

  The illumination light 3, that is, the EUV raw beam 4 is incident on the first mirror BS 1 of the beam shaping optical unit 30 with strong grazing incidence. Therefore, the incident angle γ of the illumination light 3 on the first mirror BS1 of the beam shaping optical unit 30 is larger than the incident angle α. The incident angle γ accurately compensates for the beam direction difference of the illumination light 3 in the yz plane that appears on the one hand between the mirrors BS1 and BS2 and on the other hand downstream of the mirror BS5 by the illumination light 3, thereby providing a beam shaping optical unit. The main beam direction of the illumination light 3 in the yz plane after exiting from 30 is parallel to the main beam direction in the yz plane at the time of incidence on the beam shaping optical unit 30, that is, parallel to the z direction. Have a large size.

Claims (16)

A deflection optical unit (13; 35; 36; 37, 38; 39; 40) for an illumination system for EUV projection lithography,
Including a plurality of deflection mirrors (D1 to D4; D1 to D5, D1 to D6; D1 to D8), on which EUV radiation (3) is incident on the common deflection incidence plane (xz) with grazing incidence;
At least four deflection mirrors (D1 to D4) for grazing incidence having a deflection effect greater than 70 ° in combination with the deflection incidence plane (xz);
At least one of the deflection mirrors (D1 to D8) is embodied as a convex cylindrical mirror and / or at least one of the deflection mirrors (D1 to D8) is embodied as a concave cylindrical mirror;
A deflecting optical unit (13; 35; 36; 37, 38; 39; 40).   The deflection optical unit according to claim 1, characterized in that at least one of the deflection mirrors (D1; D1 to D8; D1 to D4) is embodied to be displaceable in a driven manner.   3. A device according to claim 1, wherein at least one of the deflection mirrors (D1 to D8) is embodied using a radius of curvature that is variable in a driven manner. Deflection optical unit. A beam shaping optical unit (6) for an illumination system for EUV projection lithography,
Comprising at least two groups (27, 28) of mirrors (27 _i , 28 _i ) on which EUV radiation (3) is incident with grazing incidence;
Each mirror group (27, 28) has a common group incidence plane (yz, xz),
The group incidence planes (yz, xz) of the mirror group (27, 28) are different from each other.
A beam shaping optical unit (6) characterized by the above. All mirrors (28 ₁ , 28 ₂ ) of one of the mirror groups (28) are downstream of the first mirror (27 ₁ ) of the further mirror group (27) and the further mirror group ( 27. Beam shaping optical unit according to claim 4, characterized in that it is arranged in the beam path upstream of the last mirror (27 ₂ ; 27 ₃ ) of 27). The angle of incidence (α) of the EUV radiation on all the mirrors (27 _i , 28 _i ) in the mirror group (27, 28) is of the same size. The beam shaping optical unit according to claim 4 or 5. Incidence of the EUV radiation (3) on at least two mirrors (27 ₁ , 27 ₂ ; 28 ₁ , 28 ₂ ; 27 ₁ , 27 ₂ , 27 ₃ ) of one of the mirror groups (27, 28) The beam shaping optical unit according to claim 4 or 5, characterized by having different angles (α, β; α, β, γ).   When projected onto the group incidence plane (xz) of the mirror group (27) at different angles of incidence (α, β; α, β, γ), the generated EUV collective output beam (7) is The beam shaping optical unit according to any one of claims 4 to 7, characterized in that it travels in the same direction (z) as the EUV raw beam (4) incident on the beam shaping optical unit (30). A beam guiding optical unit (10) for an illumination system for EUV projection lithography comprising:
A focus assembly (14; 41; 45; 46; 49; 52; 55) for transmitting each EUV individual output beam (9 _i ) into the intermediate focus (42) of the beam guiding optical unit (10);
A beam guiding optical unit (10) characterized by the above. The focus assembly (14; 41; 45, 46; 49; 52; 55) comprises at least two mirrors (47, 48; 50; 51; 53, 54), i.e. at least one ellipsoidal mirror (47; 50; 54)
On the other hand at least one parabolic mirror (53) or at least one hyperboloidal mirror (48; 51);
The beam guiding optical unit (10) according to claim 9, characterized by comprising: An illumination system for EUV projection lithography,
A beam shaping optical unit (6) for generating an EUV collective output beam (7) from an EUV raw beam (4) of a synchrotron radiation-based light source (2);
An output coupling optical unit (8) for generating a plurality of individual EUV output beams (9 _i ) from the EUV collective output beam (7);
In each case, it comprises a beam guiding optical unit (10) for guiding the respective EUV individual output beam (9 _i ) towards an object field (11) where a lithographic mask (12) can be placed,
An illumination system characterized by that. The beam shaping optical unit (6)

The EUV collective output beam (7) having an aspect ratio contribution of
The output coupling optical unit (8) and / or the beam guiding optical unit (10) is followed by a number N of EUV individual output beams (9 ₁ , 9 _N ) each having a 1: 1 aspect ratio contribution. Embodied to generate,
The illumination system according to claim 11.   13. Illumination system according to claim 11 or 12, characterized in that it comprises an EUV light source (2). A projection exposure apparatus (1) for EUV lithography comprising:
The illumination system according to any one of claims 11 to 13, comprising:
A reticle holder (20) for mounting the reticle (12) on which the illumination light (3) of the optical system is incident on the object field (11);
A projection optics unit (19) for imaging the illumination field (11) into the image field (22) in the image plane (23);
During projection exposure, the wafer (24) is placed on the image plane (23) so that the reticle structure located in the object field (11) is imaged onto the wafer section located in the image field (22). Including a wafer holder (25) for mounting;
The projection exposure apparatus (1) characterized by the above-mentioned. A method for generating a structured component, comprising:
Providing a reticle (12) and a wafer (24);
Projecting the structure on the reticle (12) onto the photosensitive layer of the wafer (24) using the projection exposure apparatus (1) according to claim 13;
Generating a microstructure or nanostructure on the wafer (24);
A method comprising the steps of:   A structured component generated according to the method of claim 15.

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